Mosaic 7.5-minute Digital Raster Graphic (DRG) Images [Illinois]
Description:
This is a statewide ArcSDE Raster Mosaic of USGS DRG images of 7.5-minute topographic quadrangles occurring in Illinois. These are unmodified DRG images as distributed by the USGS, except (1) collar information has been removed for map tiling and (2) the data have been reprojected to the customary ISGS Lambert Conformal Conic projection (NAD 27). The map scale is 1:24,000. The map units are meters. The images were scanned at 250 dpi, giving an approximate raster cell resolution of 2.5 meters.